Two important features of atherosclerotic plaque progression are the presence of large necrotic cores,[unreadable] which arise from macrophage (Mf) death, and inflammation. In addition, advanced lesional Mfs accumulate[unreadable] large amounts of free cholesterol (FC). Using cultured Mfs, we have shown that FC loading induces[unreadable] inflammatory cytokines and activation of p38 MARK and the unfolded protein response (UPR). This is[unreadable] followed by down-regulation of the anti-apoptotic protein Bcl-2, induction of UPR/p38-mediated apoptosis,[unreadable] and, in the absence of phagocytosis, secondary cellular necrosis. Importantly, markers of the UPR are[unreadable] associated with Mfs in advanced atherosclerotic lesions. In this context, we hypothesize that Mf apoptosis[unreadable] and inflammatory responses in advanced atherosclerotic lesions, coupled with defective phagocytic[unreadable] clearance of the apoptotic cells, promote progression to the vulnerable plaque. To test this hypothesis, we[unreadable] will explore the role of the MKK3-p38 MAP kinase pathway in cholesterol-induced Mf death in vitro and in[unreadable] vivo (Aim I); investigate the FC-induced inflammatory response and the consequences of phagocytic[unreadable] clearance of FC-loaded Mfs (Aim II); and determine the role of Bcl-2 in FC-induced Mf apoptosis and plaque[unreadable] vulnerability (Aim III). Each Aim will consist of a series of mechanistic experiments using cultured Mfs and,[unreadable] to determine relevance to plaque morphology, in-vivo experiments using mice with targeted mutations in[unreadable] critical genes in the aforementioned pathways: macrophage p38; the apoptotic cell phagocytic receptor[unreadable] Mer; and macrophage Bcl-2. These studies will involve essential interactions with each of the other projects[unreadable] of the program as well as use of the Lesion Analysis Core and biostatistic and QPCR core functions. The[unreadable] ultimate goal is to elucidate how FC-induced apoptosis and inflammatory cytokine production in Mfs and[unreadable] phagocytic clearance of apoptotic cells affect those late lesional characteristics that eventually lead to[unreadable] atherothrombotic vascular occlusion. New insights in this area may suggest new therapeutic strategies to[unreadable] combat cardiovascular disease.